What fraction of an asteroid makes it to the earth’s surface

(ORDO NEWS) — When a small asteroid enters the Earth’s atmosphere, its surface becomes very hot, causing it to melt and fragment.

Thus, the reason why rocks from the surface of an asteroid reach the earth in the form of meteorites remains a mystery.

That mystery has finally been solved in a new study of the atmospheric combustion of asteroid 2008 TC3, published today in Meteoritics and Planetary Science.

“Most asteroid-falling meteorites are about the size of a grapefruit or a small car,” said lead author and meteorologist Peter Jenniskens of the SETI Institute and NASA’s Ames Research Center.

“Rocks this size can’t spin fast enough to distribute heat during the brief meteor phase, and we now know that it’s the backside that survives to make contact with the ground.”

In 2008, a 6-meter asteroid called 2008 TC3 was discovered in space and tracked for over 20 hours. It entered the Earth’s atmosphere, creating a bright meteor effect, and disintegrated over the Nubian Desert, Sudan. Subsequent crushing scattered the meteorites over an area of ​​7 x 30 km.

Jenniskens, along with Khartoum University professor Muawiyah Shaddad and his students, found and collected these meteorites.

“During a series of specific searches, our students found more than 600 meteorites, some the size of a fist, but most no bigger than a thumbnail,” says Shaddad. “We have fixed the location where each meteorite was found.”

By searching the grid perpendicular to the asteroid’s trajectory, the researchers found, to their surprise, that more large meteorites were scattered than smaller meteorites. Teaming up with NASA’s Asteroid Threat Assessment Project (ATAP) at NASA’s Ames Research Center, they decided to investigate.

“As the asteroid approached Earth, its brightness fluctuated due to rotations and shaking,” said Darrell Robertson, a theoretical astronomer at ATAP. “Because of this, asteroid 2008 TC3 is unique in that we know its shape and orientation as it enters Earth’s atmosphere.”

Robertson created a hydrodynamic model of 2008 TC3’s entry into the Earth’s atmosphere. It shows how the asteroid heated up and disintegrated. The observed brightness heights of meteors and dust clouds were used to calibrate the height of a model of this phenomenon.

“We found that due to its high speed, the asteroid left an almost vacuum trail in the atmosphere,” says Robertson. “The first fragments came from the sides of the asteroid and tended to follow, where they mixed and fell to the ground at low relative velocities.”

When falling to the ground, the smallest meteorites, stopped by the effect of friction, fell close to the split point, while larger meteorites could not stop and fell further. Thus, most of the collected meteorites were found along a small strip 1 km wide along the path of the asteroid.

“The asteroid heated up more and more from the front, and eventually the surviving part from the rear underside of the asteroid suddenly broke off and broke into many pieces,” Robertson said. “The back end lasted so long thanks to the shape of the asteroid.”

No longer under the control of the asteroid itself, the last fragments were breaking off and flying away from it at a much greater relative speed.

“The large meteorites from 2008 TC3 were scattered over a wider area than the smaller ones. This means that they came into being as a result of this ultimate destruction,” Jenniskens said.

“Based on the location of the discovery, we concluded that these pieces remained relatively large until the very impact with the ground.”

The location of large meteorites on the ground still reflects their location at the back bottom of the original asteroid.

“This asteroid was a collection of different rocks,” said co-author Kierena Goodrich of the Lunar and Planetary Institute (USRA). Goodrich led a team of meteorite researchers who determined the meteorite type of each found fragment in a region of high mass.

The researchers found that different types of meteorites were randomly scattered across the earth and therefore were also randomly distributed on the original asteroid.

“This is consistent with the fact that other meteorites of this type, although on a much smaller scale, also contain random mixtures,” said Goodrich.

These results may also help understand other meteorite falls. Asteroids, while in space, are exposed to cosmic rays, thereby creating a low level of radioactivity on the surface.

“Because of this radioactivity, we often learn that the meteorites were not in the more protected interior,” Jenniskens said. “Now we know that they are falling from the surface of the back of the asteroid.”


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